Vascular access for establishing an extracorporeal blood circuit is typically obtained by using a trans-dermal needle or a luer connected catheter. Usually blood processing treatment routines require establishment of extracorporeal blood circuits. Examples of blood processing treatment routines include continual renal replacement therapy such as hemodialysis wherein blood flows outside a patient's body via a set of tubes, commonly known as arterial supply line, to a dialyzer (artificial kidney) which removes waste products and excess fluids from it. Uncontaminated blood, then, flows back into the patient's body via a second set of tubes commonly referred to as venous return line.
An extracorporeal blood circuit might be disrupted while a blood processing treatment routine is in progress due to disconnection of a needle or a catheter providing vascular access. Such disruption may have serious and often fatal consequences. Needles corresponding to an arterial supply line or a venous return line of a blood circuit may disconnect due to numerous reasons, including the sudden movement of the patient undergoing the blood processing treatment. Disconnection of a supply line is relatively easy to detect by monitoring air in the supply line. In circumstances where a supply line disconnection remains undetected for some time, generally, only a slight blood loss occurs, which is equivalent to that caused by a small needle wound.
Disconnection of venous return line of an extracorporeal blood circuit is a much more alarming occurrence. The blood flow rate in most blood processing treatment routines such as hemodialysis is very high, typically around 300-400 ml/min. Hence, a disconnection of a venous return line results in blood being pumped out of a patient's body at a rapid rate. Multiple liters of hemorrhaging within a few minutes lead to serious injury and may cause death, if not detected and remedied immediately.
Detection of a return line disconnect is difficult, as most known methods are based on monitoring and detecting a change in pressure in the venous return line tubing. Return line disconnection usually occurs due to a needle pull out situation. Since, a needle typically offers the highest fluidic resistance in an extracorporeal blood circuit, a pressure change in the return line due to needle disconnect is not significant and cannot be detected easily. The pressure drop is also very low in cases where a catheter disconnects from a patient's body, causing a return line disconnection.
Hence, detection of a disconnection in a return venous blood circuit using pressure as an indicator or metric is unreliable and may result in serious injury. Further, methods using detection of air bubbles as an indication of a disconnect cannot be relied upon because a disconnect in a venous return line does not cause air to be drawn in the return line tubing.
One known method uses a detection of moisture at a needle site to detect the disconnection of a venous return line of an extracorporeal blood circuit. The method is based on an assumption that a needle pull out would cause a blood leak, thereby making the needle site wet. Various moisture sensing methods are available for use in the detection of moisture at a needle site. One such method employs optical spectrophotometry and another employs electrical conductivity measurement for moisture detection.
Moisture sensing methods require an additional apparatus, such as sensor elements to be fastened to a patient's body near the needle site. Further, such methods are based on the assumption that, after a needle pull, blood is pooled near the sensor element. However, in situations where the needle pull out is caused by a violent action, such as sudden rolling over of the patient while sleeping, the needle may cause blood flow at a distance from the sensor element. Hence, in such a situation, the moisture sensing method would provide a false negative and, at approximately 300 ml/min blood flow rate, excessive blood loss would occur in only a couple of minutes.
Another known method uses detection of certain signals from a patient's body for detection of disconnection of venous return line. This method detects changes in signals which are attributable to a needle pull out from a patient's body. One method measures electrical signals of a patient's heart through a return venous line of an extracorporeal blood circuit of the patient. In a needle pull out situation, the electrical signals are no longer detectable. This method takes advantage of the fact that blood is a good electrical conductor and the electrical signals generated by the patient's beating heart are conducted through blood carrying tubes as long as the extracorporeal blood circuit is unbroken.
However, the method fails in situations where a needle pull out occurs causing bleeding but the return venous line is intact due to fluid contact with the pool of blood. Also, efficiency of the method decreases due to the fact that the electrical activity of heart provides a very small electrical signal which, in a noisy electrical background, yields a low signal to noise ratio. Hence, loss of the signal or a failure to distinguish it from a noisy background may cause a false positive reading.
Consequently, there is need for an improved apparatus and method for detecting a disconnect in a venous return line. Further, there is also need for an apparatus and method which does not require any extra element, such as a moisture pad to be placed at the needle insertion site. Hence, there is need for an apparatus and method for detecting a disconnect in a venous return line of an extra corporeal blood circuit, which is reliable and reduces the probability the disconnection remaining undetected and causing fatal consequences.